1. Field of the Invention
The present invention relates to a fuel tank cap with a pressure control valve for controlling pressure in the fuel tank and method of manufacturing the same.
2. Description of the Related Art
One known example of fuel tank caps is disclosed in JAPANESE UTILITY PATENT PUBLICATION GAZETTE No. 6-88606. FIG. 38 is a sectional view illustrating a fuel tank cap 300. As shown in FIG. 38, the fuel tank cap 300 includes a plastic casing body 302 screwed to a filler neck FN of a fuel tank (not shown), a cover member 330 attached to the casing body 302, and a negative pressure valve 340 received in a valve chamber 304 of the casing body 302 for controlling pressure in the fuel tank. The negative pressure valve 340 includes a rubber valve body 342, a valve supporting member 346 with a fitting aperture 346a for supporting the valve body 342, and a spring 348 for pressing the valve body 342. When the differential pressure between the tank pressure and the atmospheric pressure applied to the valve body 342 increases to or above a predetermined level, the negative pressure valve 340 opens to make the tank pressure approach atmospheric pressure.
The cover member 330 is detachably and rotatably attached to the casing body 302. The attachment-detachment mechanism includes four flange members 308 that are arranged along the circumference of the casing body 302 and formed to extend outward in the radial direction of the casing body 302, and an engagement projection 334 that is formed on an inner wall of the cover member 330. The cover member 330 is pressed onto the flange members 308 of the casing body 302, which then ride over the engagement projection 334. This enables the cover member 330 to engage the casing body 302.
The engagement projection 334 is projected from the inner wall of the cover member 330. Since this portion is undercut in injection molding, a slide mold is used for manufacturing the cover member 330. A split trace of the slide mold is formed on a bottom wall 332 of the cover member 330. When the cover member 330 is rotated relative to the casing body 302 via a ratchet mechanism 320, the split trace is slid to cause shavings.
The cover member 330 is manually operated to open and close, and is required to have an additional function, for example, the function of quickly discharging electricity when the user who is electrostatically charged manually touches the cover member 330 in a dry atmosphere.